The million dollar question (definitely pun intended. Lolz)!!! Well, like most people who travel, I've also been posed with this question time & again. Money doesn't grow on trees, right? So, how to travel with minimal spending, esp., in Europe which is so damn expensive!!!
There are, ofcourse, the most obvious things including, look for 'things to do free of cost' wherever you go like 'seeing' Eiffel Tower or Atomium doesn't cost a thing and only climbing it needs a ticket; staying in hostels or couchsurfing or budget hotels; taking the 'free walking tour', traveling by public transport, eating in cheap-eats etc! So I'm just gonna skip them!
1. Backyard Tourism - I can't recommend this enough! Let me lend a para from my earlier post - "Several Indians, dream of a photograph near Eiffel Tower while several Europeans dream of the colors, festivity and sand of Rajasthan! Why not, we just put ourselves in the other person's shoes and try to explore what's close to us than the opposite side of the globe." While going out & exploring new places as frequently as possible is our wish, it can't be on the opposite side of the planet! Many of my travels are weekend destinations from where I live. My doctor in Brussels once told me that I've seen more of Belgium than she has and she belongs to Belgium! Buy 1-2 multi-site annual passes (English Heritage pass, Museumpassmusees etc) and explore your own backyard! You'll see how the landscape and culture completely changes every 50km!
2. Mi casa es tu casa - Its a beautiful Spanish phrase which means 'my house is your house'! Head to places where your friends are living and return the favour, by playing host to them when they visit your city/town/village! That ways, one of the major expenses - hotel - is completely averted & another major expense - food - is partially averted, plus you'll catch-up with your friends and have a great time!
3. Let the railways/airlines decide the destination - With a well-connected railways and cheap flights of Ryanair, Wizzair etc, it always works out cheaper to let them decide the destination. Early-bird tickets to Cologne in Thalys is as low at €19 and once I flew London <=> Copenhagen at £19! Did I have a wishlist in which I struck off Cologne & Copenhagen? No. I just went with the flow, and decided to head to Cologne or Copenhagen just because of cheap trains/flights! With fixed destinations, it works out much more difficult to make it cheap as well!
4. Cook! - I hate cooking. I really really hate cooking. When I met this probable boyfriend, years ago (who is now my husband!), one of the first things I informed was that I hate cooking! But, do I hate cooking so much as to sacrificing travel? Nope... What's the connection? Well, cooking is cheaper than ordering-in or eating-out! If we're in absolutely no mood to cook, we buy frozen food from super market and not a restaurant! Nowadays, we even book Airbnbs with kitchen and carry a couple of basic stuff like our Indian masalas, MTR Puliogare mix, a few Haldiram's ready to eat gravies; and buy rice, chopped frozen vegetables and tortilla wraps at our destination. The above pic is in Malta, our packed lunch of Puliogare rice at the beach!
5. Lifestyle - Finally, the point that everyone who travels, re-iterates, again & again - traveling is a lifestyle choice. I buy new clothes at sale or from flea-markets and only very few; I own 4 pairs of shoes and 3 hand-bags (which is so unlike how I was a decade ago) and have no intention to buy more until any of these give-up. We don't have Netflix. We do some of our shopping, esp., for toys etc in Facebook Marketplace! We don't buy hoards of gold jewelry - which is a very common practice in India, for investment! We don't throw parties and said above, we don't eat out much! Sometimes people are even offended because my daughter is wearing 'simple' clothes, but we choose to turn a deaf-ear to them as well!!! We 'choose' to spend on travel..... 
