See above for my posts to Oscar and Steve on the best place to buy your grandstand tickets and some party options.
Sector Rocher is the cheapest ticket type in Monaco but it is a hillside overlooking the track, not for everyone!!
Grandstands are the next cheapest and K1, K2 (high) in my opinion are the best but T (high) is also ok as it lets you see into the pits – not as extensive a view as K though. B in Casino square is ok also if you like seeing the various different line the drivers take on the same corner…personally I think K has more to offer if you were to pick just one stand, or you could go for a different grandstand each day to get a variety of views.
Then you have non-catered balconies which are a little more expensive than grandstands (better than grandstands with cover from the elements, better views, open bar etc, and you can bring your own food – this keeps the cost down as there are no chefs/catering/etc).
Of course there are also full hospitality balconies, yachts, etc. etc. but as you might expect these are all more expensive than grandstand tickets so might be outwith your budget.
You can get some parties, on yachts or at other locations, at the last minute but to be honest they tend to fall into the ‘you get what you pay for’ category. We offer yacht parties with open bar, canapes, music, dancing, hostess service etc. but there are also lots of bars and restaurants in Monaco.
You can also get hospitality at the last minute from street touts but you have to be really careful, I’ve now lost count of the number of times I’ve heard some of them try to oversell a location or a view or similar to unsuspecting guests.
It all really boils down to where best to spend your budget, for sure I would recommend staying outside of Monaco to save on your accommodation leaving you more to spend on your tickets, partying etc.
Have a read of the other posts for the links and advice and if I can help at all to point you in the right direction or with other suggestions/recommendations to keep your budget down just let me know.